The present invention relates to a sealing system which uses a radial set packer element for sealing with a wellhead, tubular, or other tool having an interior cylindrical surface. More particularly, this invention relates to a packer element which is configured to achieve an initial seal between a wedge ring and the cylindrical surface with an first elastomeric seal body, so that the subsequent application of fluid pressure results in the seal element moving further relative to the wedge ring to sealingly engage a second seal body, which has a lower elasticity than the first seal body, with the cylindrical surface. In response to fluid pressure, both the second seal body and one or more radial extending ribs of the packer element may be moved into sealing engagement with the cylindrical surface, thereby forming a reliable high pressure and/or high temperature seal.
Annular seal assemblies, also called packer elements, have been used to seal between a wedge ring having a conical outer surface and a cylindrical sealing surface. A positioner, which in some applications is a conveyance tubular for lowering the packer element into the well, is manipulated axially either to move the packer element relative to the wedge ring, or to move the wedge ring relative to the packer element, thereby radially expanding the diameter of the packer element from an initial reduced diameter position to an expanded diameter sealing position.
U.S. Pat. Nos. 4,757,860 and 5,076,356 disclose radial set packer elements which may be used in various applications, including a subsea wellhead. U.S. Pat. Nos. 5,511,620 and 5,333,692 disclose packer elements intended for sealing between a liner hanger and a casing. Other types of packer elements are disclosed in U.S. Pat. Nos. 5,685,369, 5,375,812, 5,110,144, 5,067,734, 4,911,245, 4,823,871, 4,771,832, and 4,719,971.
In a subsea wellhead application, an annular seal assembly or packer element has thus been used to seal the annulus between the cylindrical inner surface of the wellhead housing and the conical or tapered outer surface on the wedge ring of the casing hanger. The packer element is conventionally run-in with a tool which also carries and lands the casing hanger within the wellhead housing. The tool may be manipulated by setting weight down on the tool to cause the packer element to radially expand and seal between the tapered wedge ring surface of the casing hanger and the cylindrical interior surface on the wellhead. After the packer element is set by this manual procedure, the blowout preventer (BOP) may then be closed around the drill pipe to increase fluid pressure applied above the packer element through choke and kill lines. This fluid pressure increase causes the packer element to further move down the taper of the wedge ring on the casing hanger. After the packer element is fully set and landed on top of the casing hanger, fluid pressure may be applied to test the integrity of the packer element at the intended working pressure of the wellhead system.
Conventional packer elements have performed reasonably well in subsea systems at normal temperatures to about 250xc2x0 F. In many applications, however, packer elements are intended to seal at elevated temperatures of 350xc2x0 F. or higher, particularly during production operations subsequent to drilling operations. Conventional packer elements with elastomeric seal bodies cannot reliably seal at sustained temperatures of 350xc2x0 F. or higher. Elastomeric material seal bodies have undesirable properties, such as high thermal expansion, high compression, high temperature degradation, and degradation in the presence of conventional drilling and/or production fluids. Also, conventional elastomeric seal bodies do not reliably seal against high pressure gas commonly produced from many wells.
If an all-metal packer element is used, the undesirable properties of the elastomer are avoided. However, it is difficult for an all-metal radial set packer element to achieve an initial seal during the setting operation. It is difficult and expensive to create the high forces required to reliably bring an all-metal radial set packer element into sealing engagement. Moreover, high set down forces may not be available due to limited drill pipe lengths in shallow wells. Due to the disadvantages of the all-metal packer elements, increased emphasis has been placed during the past decade or more to reduce the undesirable properties of the elastomeric seal bodies. While a change in the elastomeric seal body material has helped in some applications, many applications continue to use packer elements with elastomeric seal bodies, and take other measures to try to minimize the detrimental properties of those seal bodies. The effort to reduce the undesirable properties of elastomeric material seal bodies in packer elements has produced limited success, particularly in high temperature and/or high pressure applications.
The disadvantages of the prior art are overcome by the present invention. An improved sealing system is hereinafter disclosed with a radial set packer element which uses a positioner to form an initial seal with an first elastomeric seal body, so that fluid pressure forces may be subsequently used to move the packer element to its expanded diameter sealing position, wherein a second seal body and optionally one or more metal ribs form a reliable seal with the interior cylindrical surface.
In a suitable subsea wellhead application, the sealing system of the present invention seals between the generally interior cylindrical surface of the wellhead and the wedge ring of a casing hanger positioned within the wellhead. The axially extending packer element includes a first seal body axially supported on a first metal rib (seal support) extending radially from a metal base, with the first seal body having an outer diameter for initial engagement with the interior cylindrical surface of the wellhead. A second seal body is axially supported on a second metal rib (seal support), with a second seal body being formed from a tin alloy or other material having a lower elasticity than the first seal body. The wedge ring on the casing hanger has a substantially conical outer surface configured to radially expand the packer element from a reduced diameter initial position to an expanded diameter sealing position. A positioner moves either the packer element or the wedge ring relative to the other of the packer element and wedge ring, such that the positioner causes the elastomeric first seal body to initially seal with the interior cylindrical surface. Due to the sealing engagement of the first seal body with the sealing surface, hydraulic forces and/or mechanical forces created by the hydraulic forces further moves the packer element with respect to the wedge ring to bring the second seal body into sealing engagement with the interior cylindrical surface. If desired, hydraulic forces may also be used to bring one or more metal ribs into sealing engagement with the cylindrical surface.
It is an object of the present invention to provide a sealing system with an improved radial set seal element which has an elastomeric seal body which creates an initial seal to assist in moving the seal element to its expanded diameter position, such that a second seal body with a lower elasticity then engages the interior cylindrical sealing surface. According to the method of the present invention, a set-down weight may be applied by a positioner for moving the seal element to form an initial seal between the first elastomeric seal body and the cylindrical interior surface. In one subsea wellhead application, the BOP may then be closed around the drill pipe and pressure applied through choke and kill lines to exert a hydraulic force on the initially set packer element to move the packer element to its expanded diameter sealing position. In another application, once the first elastomeric seal body seals with the cylindrical interior surface, the BOP may be closed and hydraulic force converted by an intensifier to a substantial mechanical force to push the packer element to its expanded diameter sealing position.
It is a further object of the present invention that at least some of the forces used to move the seal element to its fully expanded diameter sealing position are exerted by hydraulic pressure created after the elastomeric seal body initially engages the cylindrical surface.
It is a feature of the invention that the packer element may be moved to its expanded diameter sealing position by positioning the first elastomeric seal body below the second seal body, such that the first seal body effectively pulls the sealing element downward along the taper of the wedge ring and to the expanded diameter sealing position. A related feature of the invention is that the first elastomeric seal body is not required to maintain a seal with the cylindrical sealing surface after the second seal body has been moved into sealing engagement with the cylindrical surface. It is thus acceptable that the first elastomeric seal body may become disabled after the setting operation is complete, provided that the disabled first seal body does not interfere with the performance of the second seal body.
A still further feature of the invention is that the packer element may be provided with metal ribs which extend outwardly from a metal base, such that the metal ribs support the seal bodies to prevent extrusion, and also may form a reliable metal-to-metal seal with the cylindrical surface after sealing engagement of the second seal body.
Another significant feature of the invention is that a relatively low set-down weight may be used to initially set the first elastomeric seal body, thereby avoiding the cost and reliability problems associated with using a high set-down forces, which may not be available due to limited drill pipe lengths in shallow wells.
Yet another feature of the invention is that the elastomeric seal body may have an initial outer diameter which is less than the internal cylindrical surface, so that the packer element may engage the cylindrical surface only after some radial expansion of the packer element due to axial movement of the packer element relative to the wedge ring.
It is a particular feature of the present invention that the packer element may form a reliable high pressure seal for operating at a temperature of at least 350xc2x0 F. between an inner cylindrical surface of a tubular or another tool and a wedge ring radially inward of the packer element.
Yet another feature of the invention is that the packer element is configured such that high temperatures do not cause high pressure buildup between the radial extending ribs of the packer element.
An advantage of the invention is that the sealing system may be used in various applications, including sealing between a cylindrical internal surface on a subsea wellhead and a wedge ring on a casing hanger, or between the internal cylindrical surface of a surface wellhead and a casing hanger, or between a casing and a liner hanger, or between a tubing hanger and a wellhead hanger. In each application, an outer tubular is connected to the internal cylindrical surface to be sealed, which may be part of a tubular or another tool, such as a wellhead assembly. The wedge ring is configured to radially expand the packer element from a reduced diameter initial position to the expanded diameter sealing position. The wedge ring accordingly may be interconnected with another smaller diameter tubular, so that the packer element effectively forms a seal between the outer tubular and the inner tubular.
A significant advantage of the present invention is that the packer element may be reliably used in high temperature applications of 350xc2x0 F. or more and/or in high pressure applications. Also, the packer element need not use exotic elastomeric materials which have reduced undesirable properties, since the elastomeric seal body is not relied upon to maintain sealing engagement once the packer element is expanded to its sealing position. The second seal body may be formed from various materials having a lower elasticity than the first seal body, including tin, tin alloys, metals softer than the metal base of the packer element, relatively hard elastomeric materials, and plastic materials.
These and further objects, features, and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.